The present invention is directed to a toughened cocontinuous resin system comprised of thermoset and thermoplastic components and a single and/or plurality of particulate toughening agents. The particulate toughening agents provide improved toughness to impact phenomena while maintaining the other properties of the composite resin system.
It is known in the composite resin art that certain additives improve the properties of composite materials. The addition of a thermoplastic component has been shown to increase toughness in a cocontinuous phase morphology as disclosed in U.S. patent application Ser. No. 391,279now abandoned filed Aug. 8, 1989 herein incorporated by reference as filed. High strength fiber additives have also been used to increase composite toughness as is well known to those skilled in this art.
Recently, elastomeric additives have been introduced into composite resin systems and have been shown to improve properties. U.S. Pat. No. 4,783,506 discloses the use of infusible particles which are claimed to improve toughness in epoxy resin systems with a continuous and discontinuous phase matrix system. U.S. Pat. No. 4,977,218 discloses carboxylated rubber particles as tougheners for composites. European patent application 87311364.1 discloses an additive particle comprised of a semi-interpenetrating polymer-network structure to improve composite toughness.
Phase morphologies in the toughened composite resin art have been identified as comprising four distinct types. These types, identified by microscopic techniques, are homogeneous, particulate, phase inverted, and cocontinuous. A homogeneous morphology is defined essentially as lacking identifiable structures at a certain magnification. A particulate morphology is defined as specks of a discontinuous phase surrounded by a larger continuous phase. Phase inverted morphology is defined as islands of a discontinuous phase in a smaller continuous phase. The cocontinuous morphology is defined as more than one phase with no discontinuous phases present. As those skilled in this art appreciate, phase morphologies are defined at comparable magnifications and that at some magnification the above distinctions may not be as clear. However, for the purposes of this art, the above defined morphologies distinguish composite resin systems.
The composite resin industry has been improving these materials over the past couple of decades and with the improvements has introduced composites to new uses. As a result of these efforts, this art is very active in continuing to improve the properties of composite materials since more of these materials are finding their way into the structures of airplanes, automobiles, and boats, which in the past have been typically constructed with other materials. The advantages of tough, light weight materials for structural uses are realized, in part, by the economy in energy savings. These materials are also found useful in sporting goods, in the production of intermediate products such as prepreg or for that matter in any use where a strong, tough, light weight material is found advantageous.